When manufacturing sails, also for competition purposes, it is an essential requirement to combine quite a number of special characteristics such as low weight, good handling qualities, low permeability to wind, high tearing resistance, elasticity, low water absorptiveness, UV resistance and similar properties. Therefore, the ultimate goal sailmakers have in mind is to create an optimized membrane for sail manufacturing which purposefully features all these characteristics.
In sail manufacturing processes it has not yet been attempted hitherto to integrate in a well-aimed manner structures into the membrane surface that improve the air resistance and aerodynamic qualities of the material. If sail membranes are made from sheets they essentially have a smooth surface. If these membranes consist of woven fabrics or composites which is frequently the case with high-grade and large-size sails the surface of the sails is characterized by structures that reflect the inherent woven material structures, as the case may be concealed by sheets, modified by coatings or changed by bonding or fusion means. While these fabric structures have an influence on the aerodynamic properties of the sails and, if applicable, their permeability to wind and water absorptiveness, they are not suited, however, to purposefully change the resistance to air.
Resistance-causing air flow or stream separation and micro-eddying will arise on both smooth as well as structured surfaces that are facing the wind. By purposefully creating microroughness on said surfaces the resistance can be reduced. Roughness in this context is particularly microroughness that brings down the degree of turbulence in the turbulence layer in relation to the surface of the sail. Such microroughness has been developed for aircraft construction purposes and is preferably provided in the form of parallel grooves or flutes arranged longitudinally to the approaching air flow direction.
It is thus the objective of the invention to propose a surface structure suited to provide a sail structure with such a microroughness and utilize said microroughness with a view to lessening turbulences.